The Children's Heart Program of South Carolina is a state wide consortium of pediatric cardiologists, who care for >90% of the 4.5 million residents in the state. This consortium has all the critical elements for a center in the PHN: adequate patient volume, clinical research infrastructure, a track record of subject enrollment, and a dedication to hypothesis driven research. These elements have allowed MUSC to be a highly successful and administratively active participant in the PHN. Further, MUSC faculty have participated as PI's in a wide variety of multicenter studies, with the PI's of this proposal often acting as the lead investigator. MUSC faculty also currently directs numerous local clinical research protocols. The combined resources of patient volume, research infrastructure and dedication have enabled MUSC to be among the top subject enrollers in the PHN as well. Protocol: Randomized Trial of Aortopulmonary Collateral (APC) Coil Occlusion on Fontan Outcome. The overall strategy for managing functional single ventricle over the past 25 years has been staged surgical palliation to an eventual Fontan procedure. However, the specific approaches vary widely. The PHN Fontan study has demonstrated retrospectively that APC occlusion prior to the Fontan procedure shows marked practice variation, and no relation to later functional status, but had no data on the hemodynamic effects. A multicenter trial is proposed with the Primary Aim of evaluating whether preoperative occlusion of APCs influences acute Fontan outcome. Hypothesis: Coiling significant APCs will not be associated with a change in outcome. Primary Outcome: Fontan pressure in the first 24 hours following Fontan surgery. Secondary outcomes include additional hemodynamic parameters, duration of pleural effusions and duration of hospitalization. A total of 240 patients will be recruited and evaluated over a period of 42 months, yielding a power of 0.85 to detect significance at the p=0.05 level. The study outcome will provide an evidence basis for the need for APC coiling, leading to potential reassessment of the need for preoperative catheterization, and either more or less aggressive efforts to occlude APCs in this important patient group. RELEVANCE: The resources utilized for single ventricle patients are extraordinarily high. Therefore, determining the optimum management for improving outcomes and reducing the duration of hospitalization after the Fontan procedure should reduce morbidity and improve resource utilization. This study will provide an evidence basis for the preoperative need for aortopulmonary coiling in this important patient group.